Preparation of acrylic acid



Oct. 8, 1963 J. cloCCHETTl PREPARATION 0F ACRYLIC ACID Filed June 27.1960 INVENTOR JOHN CIOCCHETTI Marg, Wlv/ ATTORNEYS.

United States Patent Of 3,106,577 PREPARATION GFACRYLIC ACID JohnCiocchetti, Armenia, Caldas, Colombia, assigner to Acidos GrasosLimitada, Armenia, Caldas, Colombia Filed June 27, 1960, Ser. No. 40,4934 Claims. (Cl. 260-533) This invention relates to a process forpreparing acrylic Aacid by synthesis trom acetylene, carbon monoxide andwalter and provides a processin which these ingredients can be reactedwith each other in gaseous phase and in which the acrylic acid formedcan be directly separated in anhydrous condition from gaseous phase bycooling.

It has been previously suggested to 'form acrylic acid and/or its estersby reacting equimolecular amounts of C2H2, CO and H2O and, df necessary,an alcohol for toi-ming an ester. However, in these known processes thereaction is always carried out in a liquid reaction mixture whichcontains, in addition to various catalysts, water and/or an alcohol, andfrom which the acrylic acid formed has to be separated by distillationor other steps. Moreover, these known processes require the use ofrelatively high pressure.

In contrast to these known processes, the applicant has found thatacrylic acid can be obtained lfrom C2H2, CO `and H2O by contacting amixture of C2H2, CO `and H2O with silica gel as a catalyst at atemperature and for a time suicient lfor formation of the acrylic acid.The reaction can be a gas phase reaction in which reactants and productare in the gas phase and a feature of the invention is the carrying outof the reaction in this manner since in consequence of such operationrecovery of the product is facilitated. Thus, the product acrylic acidcan be recovered by cooling the gas mixture to condense the acidwhereupon anhydrous acid is recovered.

The reaction can be represented by the following equation:

The preferred temperature for the gas phase reaction is ZOO-220 C. Thepressure can be atmospheric, and, where a fluidized bed of silica gel ismaintained in the reaction zone, atmospheric plus the head loss throughthe bed.

In a preferred manner of 'operation the gas mixture of C2H2, CO and H2Ocan be cont-acted in a reaction zone with the silica gel, withdrawn fromthe reaction zone, cooled to condense product acrylic 'acid and providea condenser effluent gas mixture of C2H2, CO, and H2O and which maycontain some acrylic acid, and this condenser eilluent gas mixture canbe used tor producing more acrylic acid by contacting with silica gel.Contacting of condenser effluent fgas can be by recycling or by passing\a gas mixture serially through a iirst silica gel bed, condenser, andthen a second silica gel bed and another condenser. By operation in thelast mentioned manner high conversions can be obtained, Aand desirably,effluent Igas from the second condenser is recycled to the rst silicagel bed.

Equimolecular proportions of the reactants is a suitable condition ofoperation and no diluent is required. Thus, the invention provides ahighly eicient conversion. Further, in comparison with the knownprocedures wherein a liquid medium is employed, the method of theinvention is not complicated by necessity for separating the productfrom a liquid.

The following example describes a specific embodiment of, and a bestmode for carrying out, the invention, to which the invention is notlimited. The appended drawing illustrates, by way yof example, anapparatus in which the process of the invention can be carried out.

' preferably not more than 0.2%.

3,106,577 Patented Oct. 8, 1063 and H2O vapor, Iare introduced into andmixed in conventional manner to a uniform gaseous mixture and preheatedto 70-80 in a tank (not shown in the appended drawing). From said tank,(the reaction mixture is introduced by a fan l5 into cylindrical reactor1, the struc'- ture of which is substantially similar to that of aconventional heat exchanger tor condenser. The reactor or cylinder 1consists preferably of steel and has two plates 1a and l-b, whichcontain a suit-able number of registering holes 11, in which tubes 4made of steel with high nickel content are inserted and fastened inconventional manner. Cylinder 1 has ilanges at both ends and theseilanges are bolted Ito registering flanges of an upper chamber Z-and alower chamber 3, respectively. The gaseous starting mixture of thereactants is supplied by fan 5 to chamber 3 aand tubes 4 and the gasesreacted in tubes 4 pass to chamber 2. Instead of using nickel steeltubes, Pyrex glass tubes can be used.

Silica gel of particle size such that a -iiuidized bed of the silicatgel results upon passage of the lgas mixture therethrough, tisIcontained Within the tubes 4. The particle size can be less than about400 microns and suitable ranges of particle sizes are 400-74 microns,and 420-110 microns. f.

The silica gel can contain up to about 0.4% impurities, A gel marketedby Davidson Chemical Company, Baltimore, Md., as 'grade l2 and reportedby the manufacturer to have the following analysis has been found to besatisfactory.

The head at which the gas mixture is supplied to the tubes 4 isatmospheric plus the head loss through the tubes. The head will beproportional to the height of settled catalyst in the tubes. In thisexample a settled height 1/3 the height of the tubes and onemeter inamount is employed and the head is 300-340` of water.

The reaction zone is within the tubes 4 and is at 200'- 220 C. The heatfior maintaining this temperature is provided in part by heat resultingfrom adsorption of gas by the silica gel and :additional heat isprovided by passing water vapor or another suitable heating medium, eig.a mixture of diphenyl and diphenyl oxide, vat 180- 200 C. in the spacebetween the outer surface vof tubes 4 and the inner surface of cylinder1.

During passage through tubes 4, the gas mixture keeps the silica gel inturbulent suspension, whereby good contact between the reaction gasesand the silica gel catalyst,

as well as -a relatively rapid passage of the ygases through tubes 4 isattained.

From tubes 4 the ygases pass to upper chamber 2, in which they lose muchof their speed, whereby silica gel particles which may have been carriedalong fall downward.

From chamber 2 the reaction mixture passes through tube 6 t-o awater-cooled condenser 7, in which the gas mixture is cooled to about C.and acrylic acid is condensed and ldrops into tank :or container 8. Thegases, which still contain acrylic acid, escape from 7 through tube 9 toa second water-cooled condenser 7', in which their residual acrylic acidcontent is condensed and drops likewise into the beforementionedcontainer 8. The gaseous reaction mixture freed from acrylic acid insaid second condenser 7', passes through tube '9' to pump 5 and is fedby this pump to a second reactor -unit which consists of the sameelements and'structural parts `as the reactor unit described above, i.e.a substantially identical reactor 1, two condensers 7 and 7 and acontainer 8 for recovering the liquied acrylic acid. The heating mediumis supplied to both reactors =1, 1 through tu-bing 101 and is dischargedfrom both reactors through tubing 102.

The water for indirect cooling of condensers 7, 7', 7, 7 is fed throughtubing 103 and discharged from said condensers through tubing 104. Theacrylic acid is discharged from containers 8, 8 through tubing 105. Thegaseous reaction mixture, from which the acrylic `acid formed has beenseparated by cooling, escapes from the fourth condenser 7, on the rightin the drawing, through tube 9 and can be recycled.

The acrylic acid product is Isubstantially pure -and anhydrous and canbe crystallized by cooling to about 4-5 C.

In the foregoing example, employing equimolecular amounts of thereactants, the reaction is about ILS-30% complete in the first reactioncylinder, and about Ztl-22% complete in the second reaction cylinder.

While the mechanisms for the reaction are not surely known and while itis not desired to predicate the invention `on any theory as to thereaction or reactions involved, it has been observed that a smallquantity of formic acid is present in the eluent gases from thereactors. The overall reaction may occur in two steps, in the first ofwhich formic acid is formed and in the second of which the acrylic acidis formed from the -forrnic acid and acetylene.

While the invention lhas been described with reference to a particularembodiment thereof, various modifications and alternatives will occur tothose skilled in the art and it is desired to secure by these LettersPatent all such modifications as are within the scope of the appendedclaims.

What is claimed is:

1. A process for producing acrylic acid consisting essentially ofcontacting a mixture of C2H2, CO, and H2O with a catalyst consisting ofsilica gel at a temperature of about ZOO-220 C.

2. A process for producing acrylic acid which comprises contacting a gasmixture of C2H2, CO and H2O with a fluidized catalyst bed of silica gelparticles at a temperature of 20G-220 C.

3. A process for producing acrylic acid which comprises passing a gasmixture of C2H2, CO and H2O through a fluidized bed `of silica gelparticles maintained in a reaction Zone while maintaining thetemperature in said zone at about ZOO-220 C., whereby acrylic acid isformed in the gas mixture, cooling the eiuent gas from said reactionzone to condense :acrylic acid therefrom as `anhydrous acrylic acid andprovide a condenser eluent Vgas mixture lof C2H2, CO and H2O, andproducing more acrylic acid from the condenser effluent gas by passingit through a bed of silica gel as aforesaid.

4. A process according to claim 3, wherein the rst mentioned gas mixturecontains equimolecular -amounts 0f C2H2, and H20.

References Cited in the le of this patent UNITED STATES PATENTS2,845,451 Lautenschlager et al July 29, 1958

1. A PROCESS FOR PRODUCING ACRYLIC ACID CONSISTING ESSENTAILLY OFCONTACTING A MIXTURE OF C2H2, CO, AND H2O WITH A CATALYST CONSISTING OFSILICA GEL AT A TEMPERATURE OF ABOUT 200-220*C.